When point guard Mike Bibby has been on the floor for the Heat, Miami’s defense has surrendered 15 points per 100 possessions more than when he has sat on the bench. (We use per 100 possessions as the standard to control for potential tempo effects).

That sounds bad, but how damaging is that? Consider this: the difference between the league’s top defense (Chicago) and the league’s worst defense (Cleveland) is 12.5 points per 100 possessions. Do the math, and you find that Bibby’s defensive impact has been about three points wider than that.

With LeBron James and Dwyane Wade, the Heat have a couple of athletic and impressive perimeter defenders who can pressure the ball and get to help positions quickly. Few perimeter players can block shots like them. But that’s not how you hide a bad defender on the perimeter, you need a big man who can erase mistakes inside to pull that off well. The Lakers Derek Fisher is not a good defender but their length inside and shot blocking cover his mistakes. The Heat have Joel Anthony but he is not used regularly.

But on defense? That’s where things get ugly. For much of the season, the Heat battled the Bulls and the Celtics for the league’s best defense. Now, the Heat have slid in the ranks down to fifth place, separating themselves from the cream of the crop. What’s most interesting is when that slide started: when Bibby came into town. He made his debut Mar. 13 against the Magic when the Heat allowed 99 points on just 89 possessions, translating to a defensive efficiency far above the Heat norm. The next game? The San Antonio Spurs dropped 125 points on the Heat.

So here are the numbers with Bibby in tow. Since that Orlando game (Bibby’s debut), the Heat’s defensive efficiency (points allowed per 100 possessions) has ranked 20th in the league at 106.4, according to data from NBA StatsCube. That’s worse than Cleveland, Minnesota and Sacramento over that stretch. Before that game, the Heat’s defensive efficiency stood at 99.7, one of the very best in the league.

There is what statisticians call “noise” in the numbers, something that Haberstroh admits (for example, Bibby came in when the Heat played their string of playoff bound teams, for one). Also, Bibby’s three-point shooting has boosted the offense when he is on the floor so despite how bad the defense is the Heat still tend to slightly outscore their opponents.

But Mario Chalmers does not have this kind of defense impact. Neither did Carlos Arroyo, the man the Heat sent out to make room for Bibby.

Right now, Bibby’s offense covers the problems. But in a playoff series where teams will work to isolate and exploit him, and to take away his offensive threes, Bibby likely will become a bigger issue for Miami.

Bibby has knocked down 36 threes in the last 12 games. He’s doing fine as a stand-in for Chalmers. Obviously the Heat continue to start Mario Chalmers (when he’s back from injury) for his aggressive defense and decent offensive skills.

The link you provided comparing Miami & Boston’s defense is excellent. I’ve always thought that Boston played a style of defense that seemed to expend less energy than Miami’s D… turns out that’s very true but Boston’s D doesn’t come without its consequences– the poor rebounding rate specifically.

Although Boston, and now Chicago, play the passing lanes and have slightly more success than the Miami Heat I still think the Heat are playing the right style of D. They expend more energy to pressure the ball handler and show hard on pick & rolls and rotating out to all the shooters BUT they also have more energy because they are younger and more athletic than any team in the league. Their aggressive on-ball defense should be able to exhaust a team like Boston who has very few backup defenders for the likes of Dwyane Wade & LeBron James. Of course this is all conjecture and probably Boston will beat them again. Should be a great series.